Heat sink and electronic device employing the same

ABSTRACT

A fan-motor-incorporated heat sink effectively supplies cooling air flow in a thin electronic device having limited space above the heat sink. The heat sink enables air intake above the heat sink by positioning a fan, the fins of a heat sink substrate and the side wall of the substrate lower than the fan driving unit. The heat sink substrate and the fins are formed such that air is exhausted only in one direction. A cover is provided on the side of the heat sink substrate on which the fan driving unit is mounted and to which air is taken in to prevent exhausted air from being taken in. The structure of the electronic device is positioned close to the upper surface of the fan driving unit on the heat sink. Thus, the heat sink can be installed on a thin electronic device while improving the cooling of a heat emitting element.

This is a reissue divisional application of reissue application No.09/930,437 (now U.S. Pat. No. RE 38,382 issued Jan. 13, 2004 ), which isa reissue of U.S. Pat. No. 5,940,268 issued Aug. 17, 1999.

Notice: More than one reissue application has been filed for the reissueof U.S. Pat. No. 5,940,268. The reissue applications are application No.09/930,437, filed Aug. 16, 2001 and issued as RE38,382 (the presentapplication), and application No. 10/667,336, filed Sep. 23, 2003, bothof which are divisional reissues of U.S. Pat. No. 5,940,268.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat sink for cooling a semiconductorelement which emits much heat such as a micro processing unit (referredto as an MPU hereinafter).

2. Description of the Prior Art

Heat sinks have been used for cooling semiconductors and the like whichemit much heat. Recently, in particular, a fan-motor-integrated heatsink incorporated with a small fan is used for coping with the high heatemission of the MPU etc.

Conventional heat sinks will be described hereinafter. FIG. 8 is aperspective view of a conventional heat sink and FIG. 9 is a crosssectional view of the conventional heat sink.

In FIGS. 8 and 9, reference numeral 81 denotes an MPU that is ahigh-exothermic semiconductor element, 82 a heat sink substrate which ismounted on the MPU 81, 83 radiator fins, 84 driving means such as amotor or the like, 85 a fan and 86 a structure such as the casing of anotebook-type personal computer etc. for defining a space above the heatsink.

The operation of a conventional fan-motor-integrated heat sink havingthe aforementioned structure will be described hereinafter. Heat emittedfrom the MPU 81 is transmitted to the heat sink substrate 82 and theradiator fins 83. Air flow generated by the fan 85 rotated by thedriving means 84 is taken in between the structure and the upper surfaceof the heat sink as shown by an arrow A and passes among the radiatorfins 83 while carrying off heat therefrom to be vented from the sidesurface thereof as shown by an arrow B.

The aforementioned conventional structure had a problem that it wasimpossible for thin devices such as the notebook-type personal computerlimited in thickness to secure a sufficient space for taking in air fromabove the heat sink and consequently to secure a sufficient coolingperformance. Although the entire heat sink may be made thin for securingsufficient space, a motor capable of rotating the fan to generate asufficient amount of air flow for cooling the device required a certaindegree of thickness because of the structure of its bearing and coil, sothat the motor was structurally limited in being made thin.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a fan-motor-integratedheat sink capable of effectively supplying cooling air flow to anelement even if the same is a heat emitting element such as an MPU etc.employed by a thin device which cannot secure a sufficient space abovethe heat sink.

In order to attain the above object, the present invention obtains asufficient space for taking in air between the upper surface of the heatsink and the casing of a device by making the height of the fan andthose of the fins of the heat sink lower than the height of the uppersurface of the fan driving means such as a motor which is structurallylimited in thickness relative to the heat sink substrate. Furthermore,the heat sink substrate and the fins are formed such that air is ventedonly in one direction to compensate for the reduction of coolingperformance caused by miniaturizing the fan and the fins of the heatsink substrate, and a cover is provided on the inlet side to prevent thevented air from being taken in.

This structure enables arranging a structure above the heat sink nearlyas low as the height of the motor and consequently mounting the heatsink on a thin device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a heat sink according to a firstembodiment of the present invention;

FIG. 2 is a plan view of the heat sink according to the first embodimentof the present invention shown in FIG. 1;

FIG. 3 is a cross-sectional view of the heat sink according to the firstembodiment of the present invention;

FIG. 4 is a perspective view of a heat sink according to a secondembodiment of the present invention;

FIG. 5 is a cross-sectional view of the heat sink according to thesecond embodiment of the present invention;

FIG. 6 is a perspective view of a heat sink according to a thirdembodiment of the present invention;

FIG. 7 is a view showing the inside of an electronic device whichincorporates therein the heat sink according to the third embodiment ofthe present invention;

FIG. 8 is a perspective view of a conventional heat sink; and

FIG. 9 is a cross-sectional view of the conventional heat sink.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will be describedhereinafter with reference to FIGS. 1 to 7.

FIG. 1 is a perspective view of a heat sink according to a firstembodiment of the present invention, FIG. 2 is a plan view of the heatsink according to the first embodiment of the present invention, andFIG. 3 is a cross-sectional view of the heat sink according to the firstembodiment of the present invention.

In FIGS. 1, 2 and 3, reference numeral 1 designates a heat emittingelement such as an MPU or the like on which a heat sink is mounted forcooling, the heat emitting element 1 having, for example, in case of anMPU, usually a shape of a quadrangle such as a square, a rectangle orthe like having a side of 40 mm to 50 mm. Numeral 2 is a heat sinksubstrate, which is substantially square-shaped in outline almostsimilar to the heat emitting element 1 and which may be made of resinsuch as plastics without being limited to metals such as aluminum,brass, etc. so long as it is high in thermal conductivity as a member.The heat sink substrate 2 may be in outline of other shapes such as acircle as needed. The heat sink substrate 2 having a flat edge surfaceis mounted on the heat emitting element 1 according to a fixing method,using a bond, hooks, screws, etc. such that the flat side thereof is incontact with the upper surface of the heat emitting element 1. A sidewall 3 is provided on three other edge surfaces of the heat sinksubstrate 2, the side wall 3 being provided along the edge surfaces ofthe heat sink substrate 2 at the outer side thereof and beingsubstantially circular around the rotating axis of a fan 7, describedlater, at the inner side thereof. The side wall 3 defines the directionof air flow and the blowing-out direction thereof and serves as a fin aswell. An edge of the heat sink substrate 2 where no side wall 3 isprovided becomes an outlet 4. Numeral 5 designates a plurality ofradiator fins, which are provided substantially in parallel to theflowing out direction of air in the vicinities of the outlet 4 whilesubstantially in circular arcs each having a predetermined length withits center at the rotating axis of the fan 7, described later, in otherplaces.

Although they are arranged substantially in circular arcs according tothis embodiment, they may be arranged substantially along a spiral.Numeral 6 is a motor serving as driving means, which motor 6 is fixed tothe surface of the heat sink substrate 2 on which the radiator fins 5are provided according to a fixing method using a bond, screws, pressfitting, etc.

Numeral 7 designates an axial fan rotated by the motor 6, which fan 7 isarranged inside the side wall 3 for generating air flow to take in andblow out air. The fan 7 is made of metal having high thermalconductivity such as aluminum etc. for enhancing radiator effect.Incidentally, it may be made of resin such as plastics etc., not beinglimited to metal so long as it is high in thermal conductivity as amember. Numeral 8 is a cover for covering the edges of the heat sinksubstrate 2 where the side wall 3 is provided, which cover 8 has anopening larger in diameter than the outer diameter of the motor 6 andsmaller than the outer diameter of the fan 7 and which is mounted on theside wall 3 of the heat sink substrate 2 using a bond, screws, pressurewelding etc. Numeral 9 designates a structure such as the casing of anotebook-type personal computer for regulating space above the heatsink.

The side wall 3 is smaller in height than the motor 6. The fan 7 isprovided on the side surface of the motor 6 being shifted toward thelower end thereof, such that the upper surface of the fan 7 is lowerthan the upper surface of the motor 6, being in height between the heatsink substrate 2 and the cover 8. The fins 5 are so high as not to touchthe fan 7 thereunder while being substantially as high as the side wall3 in the vicinity of the outlet 4 and outside the fan 7. As shown inFIG. 3, even if the structure 9 is designed to be arranged close to theupper surface of the motor 6, there exists a sufficient space into whichair flows between the structure 9 and the cover 8, so that it ispossible to generate a smooth air flow by the rotation of the fan 7.

The operation of the heat sink having the above structure will bedescribed with reference to drawings.

In FIG. 3, heat generated in the heat emitting element 1 is transmittedto the heat sink substrate 2, the side wall 3, the radiator fins 5 andthe cover 8. Air flow generated by the fan 7 rotated by the motor 6 istaken in from above the heat sink as shown by an arrow A, passes throughthe opening of the cover 8 and among the fins 5 while carrying off heattherefrom toward the outlet 4 and is vented from the side surface of theheat sink as shown by an arrow B. Even in case that the upper structure9 is arranged as close as possible to the upper surface of the motor 6in order to make the device thin, the structure of the present inventioncan secure an inflow route of air since it can afford a space above thecover 8. A conventional structure employing a motor having the samethickness cannot secure a comparable amount of air flow since the inflowroute is blocked although the fan is exposed to the outside to a greaterextent than the structure of the present invention. In addition, in casethat the motor itself is made thin in the conventional structure, theinflow route of air can be secured but the reduction of motor outputcannot be avoided, so that the amount of air flow is reduced. Thus withthe structure of the present invention, an effective cooling becomespossible since the inflow route of air is secured without reducing themotor output.

Next, the operation of the cover 8 will be described with reference toFIG. 3 as well. In a heat sink having the above structure, the fan 7 canhave either of the structure of an axial fan or that of a centrifugalfan. However, since the advantage of the heat sink according to thepresent invention resides in being able to be made thin and it is mainlyused for cooling the semiconductor elements in a thin electronic device,the outer dimension of the heat sink is about 40 mm in side length andabout 10 mm in height. Therefore, the dimension of the fan in heightneeds to be limited to about 5 mm in order to secure a sufficient routefor air flow between the upper surface of the heat sink and thestructure 9. In addition, the length of a fan blade needs to be limitedto about 30 mm. Although a conventional heat sink as shown in FIG. 9usually employs a centrifugal fan such as a scirocco fan for taking inair from above and venting it in a side direction, the present inventionemploys an axial fan since a sufficient blade length cannot be obtainedfor the centrifugal fan. Without the cover 8, air flow directed downwardby the fan 7 is reversed in flowing direction by the heat sink substrate2 to escape toward the inlet through spaces among the blades of the fan7 or through space between the fan 7 and the inner wall of the heat sinksubstrate 2. Providing the cover 8 to cover a part of the fan 7 iseffective for restaining such escape. In case that the diameter of theopening of the cover 8 is larger than the envelope of the tip ends ofthe fan 7, a larger amount of air escapes toward the inlet.Alternatively, in case that the diameter of the opening of the cover 8is much smaller than the envelope of the tip ends of the fan 7, thesmall area of the inlet opening reduces the amount of inflow air. Inpractical use, since the performance varies depending on the structureinside the device such as the structure 9, the opening dimension is setto be optimal to the device.

Incidentally, although the motor 6 is mounted on the heat sink substrate2 according to this embodiment, it may be mounted on the cover 8 so asto be mounted on the heat sink substrate 2 by way of the cover 8.

A second embodiment will now be described. FIG. 4 is a perspective viewof a heat sink according to the second embodiment of the presentinvention, and FIG. 5 is a cross-sectional view of the heat sinkaccording to the second emdboiment of the present invention.

Reference numeral 11 designates a heat emitting element such as an MPUetc. on which the heat sink is mounted for cooling, 12 is a heat sinksubstrate, 13 designates a side wall provided on three edge surfaces ofthe heat sink substrate 12, 14 designates an outlet for blowing out airformed on an edge surface of the heat sink substrate 12 where no sidewall 13 is provided, 15 designates a plurality of radiator finsintegrally provided with the heat sink substrate 12, 16 is a motorserving as driving means, 17 is an axial fan rotated by the motor 16, 18is a first cover for covering the edges of the heat sink substrate 12where the side wall 13 is provided, and 21 designates a structure suchas the casing of a notebook-type personal computer for regulating aspace above the heat sink. The components described above are similar tothose according to the first embodiment, so that the description thereofis omitted. Numeral 19 is a second cover which is substantiallyquadrangular and concave in outline and one side of which is open withan inlet 20 for determining the inflow direction of air. The secondcover 19 is mounted on the heat sink substrate 12 such that the inlet 20is directed in a predetermined direction relative to the heat sinksubstrate 12.

The operation of the heat sink having the above structure according tothe second embodiment will be described with reference to FIGS. 4 and 5.The heat sink substrate 12, the outlet 14, the fins 15, the motor 16,the fan 17 and the first cover 18 have the same structures as those ofthe first embodiment set forth above, and the second cover 19 is mountedthereon. The second cover 19 has the inlet 20 at one edge surfacethereof, from which air is taken in by the rotation of the fan 17 and isblown out from the outlet 14 while passing among the fins 15 to carryoff heat therefrom. The second cover 19 can be mounted on the heat sinksubstrate 12 such that the inlet 20 is directed in a predetermineddirection, thereby realizing a heat sink which takes in air from apredetermined direction and vents the air in a predetermined direction.Thus, in case that it is necessary to cool parts emitting large amountsof heat inside a device equipped with the heat sink, it is possible totake in air from an optimal direction, thereby enabling the optimizationof the effect of cooling the entire casing containing an MPU and thelike. In addition, the structure 21 provided in the casing of anotebook-type personal computer etc. for regulating a space above theheat sink can sufficiently secure the inflow route of air even if it isin contact with the upper surface of the second cover 19, therebyeliminating the variation of performance due to the space between theheat sink and the structure 21 to facilitate designing the device.

It is possible to mount the second cover 19 on the heat sink substrateand take in air from a direction also in the conventional structure, butthe thickness of the heat sink substrate increases by that of the secondcover 19. In case that the second cover 19 is mounted on the heat sinkaccording to the second embodiment of the present invention, it ispossible to arrange the motor 16 and the second cover 19 closely to eachother, thereby realizing a thin heat sink capable of taking in air froma particular direction and venting the air in one direction. Devicesrequiring the one-direction air taking and the one-direction air ventingare mainly thin devices limited in space, so that the thin one-directionair taking and one-direction air venting heat sink having the structureof the present invention can realize a large effect.

Now, a third embodiment will be described. FIG. 6 is a perspective viewof a heat sink according to the third embodiment of the presentinvention, and FIG. 7 is a view showing the inside of an electronicdevice in which a heat sink according to the third embodiment of thepresent invention is incorporated.

Reference numeral 60 designates a heat emitting element, 61 is a heatsink similar to that of the second embodiment, 62 is an inlet providedin the heat sink 61 for taking in air, 63 designates an outlet providedin the heat sink 61 for venting air therefrom, 64 is a first ductconnected to the inlet 62, and 65 is a second duct connected to theoutlet 63. Although the figure illustrates the first duct 64 and thesecond duct 65 each having a rectangular cross section similar to thatof the inlet 62 or that of the outlet 63, they can have any shape; forexample, it is also possible that the tip end of the first duct 64 atthe side of taking in air has a shape laterally wider than the inlet 62and the tip end of the second duct 65 at the side of venting air has ashape of a circle or the like larger than the outlet 63. Alternatively,the duct can be provided only at either of the inlet 62 or the outlet63. In FIG. 7, reference numeral 70 designates the casing of anelectronic device, 71 is a printed board on which electronic parts, heatemitting elements etc. are arranged to constitute an electric circuit,and 72 is a heat emitting device such as a power supply. The first duct64 at the side of the inlet 62 has its opening in the vicinity of theheat emitting element 72 such as the power supply inside the electronicdevice, while the second duct 65 at the side of the outlet 63 has itsopening at the exhaust port of the casing 70 of the electronic device.Air flow generated by the heat sink 61 takes in air around the heatemitting element 72 through the first duct 64, passes through the heatsink 61 and is vented from the casing of the electronic device throughthe second duct 65.

The operation of the heat sink having the above structure according tothe third embodiment will be described with reference to FIGS. 6 and 7.

As shown in FIG. 7, providing the first duct 64 and the second duct 65in the heat sink enables taking in air at a predetermined position froma predetermined direction and venting the air to a predeterminedposition in a predetermined direction, thereby eliminating therestriction in the direction and position in taking in and venting aircaused by the position of the MPU or that of the printed board. Withoutthe first duct 64 at the inlet side, the heat sink 61 only takes in airon the printed board 71, but providing the opening of the first duct 64in the vicinity of a specific component, for example, the power supply72, enables taking air as well as cooling the power supply 72. Inaddition, providing the opening of the second duct 65 at the exhaustport of the casing 70 enables discharging the heat of the heat emittingelement 60 or that of the power supply 72 from the casing withcertainty, thereby preventing the heat from diffusing therein. It isalso possible to eliminate the necessity of additionally providing a fanfor exhausting air other than the heat sink in the casing, therebysimplifying the structure.

The present invention can be embodied in other various forms withoutdeparting from the spirit or main features thereof. Therefore, thepreferred embodiments set forth above are illustrated only by way ofexamples in all respects, and should not be interpreted by way oflimitation. The scope of the present invention is represented by thescope of the claims for a patent but not restrained by the specificationat all. Furthermore, the modifications or variations belonging to theequivalent of the scope of the claims for a patent are all within thescope of the present invention.

1. A heat sink comprising: a substrate having a floor and a verticalside wall open in one direction; a plurality of fins verticallyprojecting from said floor of said substrate; driving means at least apart of which is supported by said floor of said substrate; and a fanrotated by said driving means wherein: a height of an upper surface ofsaid side wall is lower than that of an upper surface of said drivingmeans relative to said floor of said substrate.
 2. A heat sink accordingto claim 1, characterized in that the fan has a shape of an axial fan.3. A heat sink according to claim 1, wherein said driving means has ahousing and said height of said upper surface of said side wall is lowerthan the height of an upper surface of said housing of said drivingmeans relative to said floor of said substrate.
 4. A heat sinkcomprising: a substrate having a floor and a vertical side wall open inone direction; a plurality of fins vertically projecting from said floorof said substrate; driving means at least a part of which is supportedby said substrate; a fan rotated by said driving means; and a platemounted to an upper surface of said side wall and having an opening,wherein: a height of said upper surface on said side wall and a heightof an upper surface of said plate are lower than that of an uppersurface of said driving means relative to said floor of said substrate.5. A heat sink according to claim 3, characterized in that the openingof the plate is so large as to allow the driving means to penetrate theplate through said opening but smaller in diameter than the fan.
 6. Aheat sink according to claim 5, characterized in that the fan has ashape of an axial fan.
 7. A heat sink according to claim 4,characterized in that the fan has a shape of an axial fan.
 8. A heatsink comprising: a substrate having a floor; a plurality of finsvertically projecting from said floor of said substrate; driving meansat least a part of which is supported by said substrate; a fan rotatedby said driving means; a plate having an opening; and a vertical sidewall structure disposed between said substrate and said plate, saidvertical side wall structure being open in one direction, said platebeing positioned at an upper surface of said side wall structure, saidplate and said side wall structure forming a frame having a height whichis lower than a height of an upper surface of said driving meansrelative to said floor of said substrate.
 9. A heat sink according toclaim 8, wherein said opening of said plate is sufficiently large toallow said driving means to penetrate said plate but smaller in diameterthan said fan.
 10. A heat sink according to claim 8, wherein said fanhas the shape of an axial face.
 11. A heat sink according to claim 9,wherein said fan has the shape of an axial fan.
 12. A heat sinkapparatus comprising: a heat sink apparatus substrate for being attachedto a heat emitting element, and having a bottom portion with a standingwall mounted thereto; a driving device supported by said substrate; anaxial fan mounted on said driving device; a plurality of fins providedsubstantially in parallel to an air flow direction that exists at an endportion of said standing wall; and a cover mounted on said standingwall, wherein said driving device protrudes through an opening formed onsaid cover and a height of an upper surface of said fan and a height ofan upper surface of said cover are lower than that of an upper surfaceof said driving device relative to said bottom portion.
 13. A heat sinkapparatus comprising: a heat sink apparatus substrate for being attachedto a heat emitting element, and having a bottom portion with a standingwall mounted thereon, said standing wall defining an air outlet, adriving device supported by said substrate; an axial fan mounted on saiddriving device; a plurality of fins provided substantially in parallelto said standing wall at said air outlet; and a cover mounted on saidstanding wall, wherein said driving device protrudes through an openingformed on said cover and a height of an upper surface of said fan and aheight of an upper surface of said cover are lower than that of an uppersurface of said driving device relative to said bottom portion.